Room modes occur due to the superposition of standing waves. In the low frequency range modal overlap tends to be negligible, and some modes can be particularly dominant. When listening to audio material in a room with strong room modes unwanted characteristics are observed, such as significant reverberation, boominess at particular frequencies, and apparent pitch changes as a tone at one frequency excites and is then dominated by a strong resonance at a slightly different frequency. These undesirable audible effects can be considerably reduced by pre-filtering the signal. This paper derives the pre-filter required and investigates the psychoacoustic criteria required to optimize the pre-filter.